Modern fully automatic and automated manual transmissions typically include a computer controlled transmission module operable to control and manage the overall operation of the transmission. A communications link, such as an SAE J1939 datalink or other hardwired analog voltage link, is established between the transmission control module and an engine control computer operable to control and manage the overall operation of an internal combustion engine driving the transmission. Certain data relating to the operation of the engine and/or vehicle carrying the engine may thus be broadcast or otherwise transmitted to the transmission module, and certain data relating to the operation of the transmission may likewise be broadcast or otherwise transmitted back to the engine control computer, via the datalink. In this manner, the transmission control module may base operation of the transmission on current engine/vehicle operating conditions.
One of the functions of the transmission control module is to control shift points of the automatically selectable transmission gears. Presently, typical transmission control modules use accelerator pedal position or percentage (often referred to as throttle percentage) during manual fueling conditions (i.e. fueling dominated by manual actuation of the accelerator pedal), as well as other engine operating signals, to control the automatic shift points. During non-manual fueling conditions (i.e., fueling conditions not dominated by manual actuation of the accelerator pedal), such as cruise control operation, power take off (PTO) operation, or other computer-controlled fueling or fuel limiting conditions, the throttle percentage does not produce an accurate indication of requested torque and the transmission controller must accordingly base shift points on some other engine operating parameter being broadcast over the datalink. Typically, transmission controllers respond to non-manual fueling conditions by basing automatic shift points on engine load or a driver requested torque parameter that corresponds to fueling conditions resulting from one or more non-manual fueling control systems.
While the foregoing transmission shift point control logic is widely used, it has certain drawbacks associated therewith. For example, engine load-based shift point control tends to result in excessive shift cycling due to the rapidly changing nature of the engine load parameter. While the driver requested torque parameter tends to produce a more stable shift point control parameter, the automatic shift point logic typically resident within the transmission control module requires unnecessary complexity since it must provide for multiple shift strategies depending upon the fueling mode currently in use.
What is therefore needed is a common parameter on which a transmission control module may base automatic shift point control regardless of the fueling mode currently in use. Such a common parameter would greatly simplify shift point control logic and possibly reduce shift cycling in systems basing non-manual fueling shift point control on engine load. Also, in applications involving computer controlled fuel limiting during manual fueling control, the common parameter should provide a more accurate estimate of throttle percentage than the actual accelerator pedal percentage itself.